Improving the strength and ductility of magnesium die-casting alloys via rare-earth addition

The development of new die-casting alloys is a multifaceted task, where success depends upon the ability to control a chain of properties, and where the weakest link determines the outcome. Optimizing one property by alloying often comes at the expense of one or more other properties. A typical example is yield strength vs. ductility. In developing alloys for high-pressure die casting, the peculiar aspects of the process must be considered. High injection speeds, high metal pressures, and the lack of efficient thermal barriers lead to extremely high cooling rates. This makes high-pressure die casting unique since the resulting refined microstructure provides excellent mechanical properties. In this article, the influence of alloy composition on mechanical properties is investigated, with special emphasis on strength and ductility. For more information, contact Per Bakke, Hydro Aluminium, P.O. Box 2560, Porsgrunn, Norway, N-3919; 47 3592 2477; fax 47 3592 2477; e-mail per.bakke@hydro.com.     

Formula relating fracture strength and fracture ductility with strength coefficient and strain-hardening exponent

To theoretically calculate the strength coefficient and the strain-hardening exponent with conventional mechanical property parameters, formulas relating them with fracture strength and fracture ductility are studied using test data for ten alloys. The applicability of the traditional formula relating these four material constants is discussed first, and then new formulas are proposed based on the premise that the traditional approach cannot be used. The main conclusions made herein are that only under certain conditions can be traditional formula be used to describe the relationship among fracture strength, fracture ductility, strength coefficient, and strain-hardening exponent; otherwise, a new formula must be used.     

Tailoring strength and ductility of high-entropy CrMnFeCoNi alloy by adding Al

High-entropy alloys with high strength and acceptable ductility at both room and elevated temperatures for high-temperature structural applications are desired....     

New nitrogen-bearing austenitic stainless steels with high strength and ductility

The effect of nitrogen on the strength, ductility, and corrosion resistance of nitrogen-bearing austenitic stainless steels is studied. Fields of application of these steels are considered.     

Ultrafine-grained pure Ti recycled by equal channel angular pressing with high strength and good ductility

Machining chips of commercially pure Ti (ASTM grade 2) were consolidated into full density by equal channel angular pressing (ECAP) with an average grain size as low as 0.8 μm, yield strength up to 650 MPa, and ductility of ～16%. Effect of recycling condition on the microstructure and mechanical properties were investigated in terms of ECAP temperature, number of passes and chemical composition. Using electron backscatter diffraction it is evident that continuous dynamic recrystallization (however, which is purely a phenomenological terminology) plays a significant role in grain (with misorientation ≥15°) formation, whilst benefitting from high stacking fault energy, this continuous conversion of subgrain (<15°) into grain can be essentially considered as an extended recovery with a substantial presence of low angle grain boundaries in the recycled Ti. The Hall–Petch relationship is adapted to explain the strengthening of the recycled Ti. Additionally, using scanning electron microscopy fractography, the ductility was analyzed by a modified Griffith criterion. Last, superior energy efficiency of ECAP reduces environmental impact when comparing to conventional melting/casting. ECAP develops an innovative solid-state process for improving the recycling value of waste Ti.     

Strength and ductility of ultrafine grained aluminum and iron produced by ARB and annealing

Strength and ductility of ultrafine grained (UFG) aluminum and iron fabricated by ARB and annealing were clarified in the grain sizes ranging from 200 nm to 20 μm. Strength held Hall–Petch relationship, while uniform elongation of the UFG materials was limited below a few percents. The limited uniform elongation in the UFG materials could be explained in terms of plastic instability.     

高强韧面心立方高熵合金的设计

钛合金因具有密度小、比强度高、耐腐蚀、可焊接等性能特点,广泛应用于航空航天、舰船、兵器、核工业等重要的工业领域。但是钛合金的成本限制了其进一步推广和大规模应用,是目前钛合金总体用量不高的核心原因。本文从原材料、合金制备技术、钛产业链单位的协作等三个方面对钛合金低成本化技术研究与发展进行了归纳和评述,在此基础上,提出了未来低成本钛合金发展的趋势和建议。     

Interaction of Freon-22 with aluminum and magnesium oxides

It is known that Freons can be destructively adsorbed by magnesium and calcium oxides under the effect of mild ultraviolet radiation. Insofar as these oxides along with the silicon, aluminum, and iron oxides are typical components of solid troposheric aerosols, photo-and dark adsorption processes may represent an efficient channel of the Freon removal from the atmosphere. In this work, dark adsorption of Freon-22 on aluminum and magnesium oxides, which were treated in a vacuum at room temperature, is studied. Experiments with the specimens that have been exposed to air for a long time are especially important in estimating the probable adsorption of a Freon on aluminum or magnesium oxide under conditions close to the tropospheric ones. Original Russian Text ? T.S. Minakova, E.B. Daibova, L.A. Savel’eva, V.S. Zakharenko, 2008, published in Zashchita Metallov, 2008, Vol. 44, No. 2, pp. 213–216.     

Optimizing the strength and ductility of fine structured 2024 Al alloy by nano-precipitation

Alloys with grain or subgrain structures refined down to 1 μm or below usually have high strength, but often inadequate tensile ductility. Past efforts in improving their ductility have usually led to a sacrifice of strength. We have developed an effective approach in achieving both high strength and high ductility in a 2024 Al alloy. The approach involves solution-treatment to partially dissolve T-phase particles, cryo-rolling to produce a fine-structure containing a high density of dislocations and submicrometer subgrains and aging to generate highly dispersed nano-precipitates. It was found that the remnant T-phase particles made it very effective in accumulating dislocations during cryo-rolling, which in turn promoted the precipitation of nanosized S′ precipitates with an interparticle spacing of only 10–20 nm. Such a high density of S′ precipitates enabled effective dislocation pinning and accumulation, leading to simultaneous increases in strength, work-hardening ability and ductility.     

Enhanced ductility in strongly textured magnesium produced by equal channel angular processing

Equal channel angular processing is shown to induce a strong deformation texture, which persists after recrystallization. The enhancement in the tensile ductility along the extrusion axis originally reported by Mukai et al. [Scripta Mater 45 (2001) 89] is discussed in terms of magnesium’s deformation mechanisms, plastic anisotropy, and the texture itself.     

电弧熔丝增材制造ODS钢的成型工艺及组织性能

采用电弧熔丝增材制造(wire and arc additive manufacturing, WAAM)技术制备了低活化铁素体/马氏体钢(reduced activation ferrite/martensite steel,RAFM钢),通过光学显微镜、扫描电子显微镜和透射电子显微镜等观察微观组织变化,通过拉伸试验进行力学性能测试,研究了热处理工艺对其微观组织和力学性能的影响.结果表明,打印态的RAFM钢微观组织为铁素体 + 回火马氏体的双相组织,平均晶粒尺寸约为1.51 μm. 经过热处理,RAFM钢的晶粒尺寸没有明显增长(1.84 μm),并在微观组织中保留了高密度位错. 此外,热处理后高数密度TiO₂二次相纳米颗粒在基体中析出,并弥散分布在基体中,其尺寸在5 ~ 10 nm. 热处理后的RAFM钢抗拉强度显著提高,断后伸长率略微下降,其室温抗拉强度为1080 MPa,在650 ℃下测试的抗拉强度仍可达285 MPa.     

多向锻造对高强度Mg-Gd-Y-Zr合金的塑性增强作用(英文)

采用多向锻造及人工时效制备高强度高塑性GW94合金。该合金具有完全再结晶组织和亚微米级超细等轴晶,其抗拉强度、屈服强度及伸长率分别为377MPa,295MPa和21.7%。与传统挤压工艺相比,多向锻造显著提高材料的塑性。在573K下拉伸时,该合金表现出超塑性,其最大伸长率为450%。GW94合金的高强度和高塑性是由完全再结晶晶粒和在晶界处动态析出Mg5(Gd,Y)纳米颗粒的共同作用。     

Improvement of strength and ductility of Al-Cu-Li alloy through cryogenic rolling followed by aging

To develop an improved approach in achieving an excellent combination of high strength and ductility, the solutionized Al-Cu-Li plates were subjected to rolling at cryogenic and room temperatures, respectively, to a reduction of 83%, followed by aging treatment at 160 °C. The results indicate that Al-Cu-Li alloys through cryogenic rolling followed by aging treatment possess better mechanical properties. Rolling at cryogenic temperature produces a high density of dislocations because of the suppression of dynamic recovery, which in turn promotes the precipitation of T₁ (Al₂CuLi) precipitates during aging. Such high density of T₁ precipitates enable effective dislocation pinning, leading to an increase in strength and ductility. In contrast, room temperature rolled alloys after aging treatment exhibit lower strength and ductility due to low density of T₁ precipitates in the grain interior and high density of T₁ precipitates around subgrain boundaries.     

Tailoring AZ91 laminates for combination of strength and ductility

Three types of laminates were designed by alternately stacking AZ91 extruded sheets in different states for extrusion to improve the mechanical properties. The tensile tests revealed that the combination of solid-solution-treated sheets with the aging-treated sheets achieved high tensile strength and ductility, i.e., ultimate tensile strength of ~386 MPa and elongation of ~19.8%, respectively. Electron backscatter diffraction (EBSD) and TEM results indicated that the aging-treated layers with more nano-sized precipitates and small grain size provided high strength and reasonable ductility, while the solid-solution-treated layers with low dislocation density facilitated strain hardening. Also, the strong interface bonding between the successive layers played an important role in the enhanced ductility.     

Increasing the strength and ductility of weldments in austenitic steels

Conclustions The same strength and ductility of the weld seam and the base metal in austenitic steels subjected to cold deformation are ensured by preliminary deformation of the seam metal (=6–8%) and hardening.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 45–47, April, 1982.     

超高强度的纯铝材料研究

本试验利用超高速多向压缩(MAC)1060工业纯铝,以制造超高强度的纯铝材料。采用Gleeble-1500热模拟试验机和冲压机进行压缩,对压缩后的试样进行硬度、拉伸试验和显微组织观察。结果表明,提高应变速度,可以显著抑制动态回复,使纯铝平均晶粒达到0.39μm,大角晶界百分数为82.9%。当以60%的道次压缩量进行超高速深度压缩时试样产生裂纹。深入研究得出,获得大角晶界超细晶粒不一定需要在全过程中都采用大的道次应变量。当位错胞壁的位错密度接近饱和值后,降低道次压缩量,可以防止裂纹产生。当伸长率相近时,其拉伸强度比H12变形纯铝材提高1.86倍。因此,超高速多向压缩技术可以生产出超高强度的工业纯铝材料。